An impact energy absorber absorbs an impact energy accompanied by an impact load from the outside due to a vehicle collision so as to protect a passenger inside the vehicle. The impact energy absorber may be disposed inside, for example, a door panel or a ceiling panel.
A conventional impact energy absorber has a first wall which is disposed in a side receiving an shock or impact, a second wall disposed apart from the first wall through a hollow portion and opposed to the first wall, and a plurality of impact absorbing ribs including a deep groove portion and a shallow groove portion. The deep groove portion is obtained by recessing the first and second walls in the form of long groove, and joining the tip surfaces of the first and second walls together to form a weld surface. The shallow groove portion is obtained by opposing the tip surfaces apart from each other. For more detail, see Patent Document 1.
However, in the case of the afore-mentioned conventional impact energy absorber as disclosed in Patent Document 1, when the impact load acts on the load-receiving surface head on, the air pressure inside a hermitically sealed hollow portion is elevated, resulting in increase in repulsion force. In this case, enough distortion of the impact energy absorber may be hardly obtained, thereby failing to obtain desired impact energy absorbing properties.
In order to overcome the above drawbacks, there has been proposed another impact energy absorber, which is a single wall, solid plate structure. The impact energy absorber is provided with a plurality of projections (i.e., impact absorbing ribs), which is obtained by forming a plurality of parallel long grooves disposed apart from each other in a planar portion. For more detail, see Patent Document 2.
However, as the impact absorber as disclosed in Patent Document 2 has less surface area of the planar portion in comparison with the surface area occupied by the projections, warpage easily occurs in the planar portion. As a result, the impact energy absorber get slightly distorted.
Furthermore, in order to overcome the drawbacks found in the impact energy absorber as disclosed in Document Patent 1, it may be also considered that the impact energy absorber is provided with a plurality of projections (i.e., impact absorbing rib), which is obtained by forming a plurality of parallel long grooves apart from each other in a planar portion and the thickness of the impact absorbing rib is modified to limit the relation of the surface area of the cross section of the impact absorbing projection within a certain range, thereby adjusting displacement due to the load.
However, as such a configuration should be applied to the plurality of impact absorbing ribs which is formed within a limited space, the impact energy absorber as a whole is necessarily further complicated and the freedom of designing or setting the impact absorbing rib is considerably compromised.